G-protein coupled receptors (GPCR) are a superfamily of integral membrane proteins which transduce extracellular signals. GPCRs include receptors for biogenic amines, e.g., dopamine, epinephrine, histamine, glutamate (metabotropic effect), acetylcholine (muscarinic effect), and serotonin; for lipid mediators of inflammation such as prostaglandins, platelet activating factor, and leukotrienes; for peptide hormones such as calcitonin, C5a anaphylatoxin, follicle stimulating hormone, gonadotropin releasing hormone, neurokinin, oxytocin, and thrombin; and for sensory signal mediators, e.g., retinal photopigments and olfactory stimulatory molecules.
The structure of these highly-conserved receptors consists of seven hydrophobic transmembrane regions, cysteine disulfide bridges between the second and third extracellular loops, an extracellular N-terminus, and a cytoplasmic C-terminus. Three extracellular loops alternate with three intracellular loops to link the seven transmembrane regions. The N-terminus interacts with ligands, the disulfide bridge interacts with agonists and antagonists, and the large third intracellular loop interacts with G proteins to activate second messengers such as cyclic AMP, phospholipase C, inositol triphosphate, or ion channel proteins. The most conserved parts of these proteins are the transmembrane regions and the first two cytoplasmic loops. A conserved, acidic-Arg-aromatic triplet present in the second cytoplasmic loop may interact with the G proteins. Most members belongs to this superfamily contain a characteristic consensus pattern. (Watson, S. and S. Arkinstall (1994) The G-protein Linked Receptor Facts Book, Academic Press, San Diego, Calif.; Bolander, F. F. (1994) Molecular Endocrinology, Academic Press, San Diego, Calif.)
Odorant receptors are members of a multigene family primarily responsible for transmission of volatile chemical signals from the environment through the olfactory neuron to cortical regions of the brain. Odorant receptors have been detected in olfactory epithelium of many mammalian species (e.g., dog, rat, mouse, and human), and a homologous family of receptors is expressed in human testes where it is responsible for sperm chemotaxis. (Parmentier, M. et al. (1992; Nature 355:453-455.)
The rat olfactory protein is a member of the odorant receptor family, and one of the first molecules to be used to investigate the molecular basis of odor recognition. (Buck L. and R. Axel (1991) Cell 65:175-187.) The rat protein is 333 amino acids in length and has a glycosylation site at N.sub.5, a palmitoylation site at C.sub.306, and disulfide bonds at C.sub.97 and C.sub.189. Homologous human olfactory receptors (OR) and OR pseudogenes have been cloned from mRNA and genomic DNA (Crowe, M. L. (1996) Gene 169:247-249).
Chemotactic receptors are important in immune responses. They are activated by chemokines, platelet activating factor (PAF), and proteases. These receptors are found on monocytes, lymphocytes, neutrophils, basophils, eosinophils, platelets and leukocytes of several mammalian species including guinea pig, rat, mouse, and human. Chemotactic receptors are widely expressed in peripheral tissues and are present in smooth muscle, lung, brain, liver, and endothelial cells.
Complement is produced in the liver, circulates in the blood and extracellular fluid, and stimulates cells to fight infections. Complement 5 (C5) is proteolytically cleaved to produce C5a and C5b whenever the complement system is activated. C5a is one of 13 plasma proteins responsible for clearing foreign particles and organisms from the blood. In addition, human C5a, a 74 amino acid peptide, functions as a chemoattractant for immune system cells.
The C5a receptor is a GPCR which is present on neutrophils, macrophages, and mast cells and is believed to interact with a Gq-/G11-protein to activate the phosphoinositol signaling pathway. The KIAA0001/C5a receptor is 338 amino acids long and has a N-glycosylation site at Asn3. (Nomura, N. et al. (1994) DNA Res. 1:27-35.)
Chariton, M. E. et al. (1997; Brain Res. 764:141-8) identified VTR 15-20, a GPCR of 305 amino acids from rat ventral tegmentum. The cDNA shares homology to several orphan receptors, and the deduced protein demonstrates the specific regions conserved among the superfamily. VTR 15-20 is expressed throughout the mammalian nervous system and in cultured rat microglia and astrocytes. The highest levels of VTR 15-20 mRNA expression were detected in peripheral tissues and spleen. Based on cellular distribution, expression in brain and spleen, and regulation as the result of immune challenge and neuronal insult, VTR 15-20 appears to play a role in neuroimmune function.
The discovery of new G-protein coupled receptors associated with immune response and the polynucleotides encoding these receptors satisfies a need in the art by providing new compositions which are useful in the diagnosis, treatment, and prevention of diseases associated with cell proliferation and cell signaling.